The invention relates to a vacuum concentrator and to a method for vacuum concentration.
Vacuum concentration is used in the chemical industry and in the laboratory, in particular within the scope of solid-liquid extraction and for drying wet, thermally unstable samples. In this connection, the fact that the boiling point of a liquid is reduced in the vacuum is utilized. As a result, the boiling liquid in the vacuum may escape from a wet sample at relatively low temperatures. To this end, the samples are arranged in a vacuum chamber which is evacuated by means of a vacuum pump. In order to prevent an uncontrolled release of liquid from the samples, said samples are arranged in the vacuum chamber in a centrifuge rotor. The heat for the vaporization is generated by means of electrical or other heating devices. The released liquid vapour is pumped off by the vacuum pump. A condenser optionally arranged between the vacuum chamber and the vacuum pump and/or a cryogenic trap arranged there, is able to capture the liquid vapour upstream of the vacuum pump, so that the vacuum pump produces a particularly strong vacuum and the drying performance is particularly efficient.
The end point of the vacuum concentration is the point in time at which the sample is dry and/or no more vaporized liquid leaves the sample. Known vacuum concentrators operate with centrifugation times which are too long in order to ensure that the liquid has completely left the sample. However, there is the risk that the samples have not been dried for long enough, so that considerable portions of residual liquid remain in the samples. It is further known to switch on the heating of the samples at the end of the concentration process once again, in order to vaporize the residual fluid by intense heating of the samples. Subsequent heating of samples which are already completely dried may lead to overheating of the samples.
Radiation heat or microwaves are used, in particular, for heating the samples as heat transmission by conduction is greatly reduced in a vacuum. Overheating of the multiple temperature-sensitive samples has to be avoided. According to DE 699 18 734 T2, the entire contents of which is incorporated herein by reference, the temperature of the vaporizing liquid samples in the vacuum concentrator is determined by the pressure during the vaporizing process being detected, an electrical pressure-data signal being generated in proportion with the sampled pressure, the pressure-data signal being transmitted to an electronic data signal processing unit, which has access to data about the volatile components present in the samples, in order to convert the pressure-data signal into a temperature value, which corresponds to the vapour pressure for the known volatile component and/or the known volatile components of the sample. In this connection, it is disadvantageous that an indication of the liquid and/or the solvent is required and the data have to be present for the relevant solvent.
Proceeding therefrom, the object of the invention is to provide an effective device and an effective method for vacuum concentration.